Polyamides that are semicrystalline are used extensively in applications that require good solvent resistance and good properties at elevated temperatures. Additionally, they are suitable for modification by reinforcing with inorganic fillers and fibers (minerals) which enhance stiffness and high temperature properties. Such reinforced polyamides are widely used as an engineering plastic molding material suitable for many applications such as automobile parts. They are ordinarily processed by injection molding, but there are many components of automobiles and other systems wherein such parts are required to be hollow, and to manufacture these by injection molding is very difficult and expensive. Many such parts can conceivably be made by blowmolding provided the polymer system has adequate melt strength and viscosity. Unfortunately, polyamides commonly used for injection molding have number average molecular weights generally between 10,000 and 25,000, which is too low to make them suitable for extrusion blowmolding. Mineral reinforced semicrystalline polyamide compositions that are available commercially, and which are described in prior art such as U.S. Pat. No. 3,846,367, have good toughness but suffer from low viscosity and low melt strength, which makes these compositions unsuitable for processing by blowmolding.
Combinations of small amounts of metal neutralized ethylene acid copolymers; e.g., "Surlyn" ionomer, with mineral reinforced polyamides have been reported to give improved surfaces on molding (U.S. Pat. No. 4,314,929). Many prior art patents claim or disclose addition of various amounts of fluoropolymer to nylon for enhancement of properties, e.g., high gloss (U.S. Pat. Nos. 4,500,603A) and wear resistance (3,879,301; 3,994,814; 2,975,128; 4,159,286). U.S. Pat. No. 3,005,795 claims addition of 0.05-20 weight percent fibrillar fluoropolymer improves the extrusion and thermoformabilities of thermoplastic resins. U.S. Pat. No. 4,491,553 discloses an improved process for making mineral filled thermoplastics in a two-step process by compounding the ingredients containing fibrillar polymer (0.01-5%) under shear without total melting, to be followed by a second step involving total melting of the thermoplastic. None of these disclose or teach the right combination of additives used with the usual injection moldable semicrystalline polyamides to result in unexpected rheological properties which make the compositions amenable to extrusion blowmolding.